This invention relates generally to a method and apparatus for ultrasonically sealing endcaps to a container for use in packaging food or tobacco products.
Methods and apparatus for sealing food or tobacco product containers constructed of dissimilar materials, for example paper and thermoplastic, have generally involved the use of wet adhesives qualified for use in the food and tobacco industry. Such adhesives may take considerable time to set sufficiently for the container to be handled by automated equipment, so that further handling of the package does not ruin the seal. Since adhesives used in the food and tobacco packaging industry must be qualified for such characteristics as toxicity, taste and odor, these characteristics have taken precedence over concerns such as the adhesive setting and drying times.
A further disadvantage inherent in using conventional glues to attach or seal food or tobacco product packages is the rate at which packages can be moved through the packaging machine. Aside from the difficulties attendant in handling the wet-glued packages, alluded to above, the time for a conventionally glued package to set can become the limiting time on a food or tobacco packaging production line, thus slowing down an assembly operation otherwise capable of much greater throughput.
Yet another disadvantage of using wet glues in packaging food and tobacco products is the tendency of the glue to smear onto and ruin the exterior of the packaging, resulting in an unacceptable end product. A need therefore exists for a method of sealing such packages which obviates the use of wet glues and which is cleaner than the previously known methods.
Accordingly, a principle advantage of the method and apparatus of the present invention is the use an ultrasonic device to seal food or tobacco containers. Ultrasonic apparatus have been used for cutting and welding plastics in numerous fields such as the automotive, electronics and medical device industries. For example, Parry U.S. Pat. No. 3,852,144 describes a method for cutting and seaming materials with a high thermoplastic content. Ultrasonic apparatus have also been used for sealing plastic and plastic covered items in the food industry because of its ability to weld through contaminated areas and its nontoxicity relative to conventional glues for sealing plastics. Bogren U.S. Pat. No. 4,606,462, for example, involves the ultrasonic welding of the plastic-to-plastic interface created during construction of a powder proof container from a plastic laminated cardboard blank. Ultrasonic devices have also found application in gluing paper and other cellulosic materials using a starch and water adhesive, as described in Johnston et. al. U.S. Pat. No. 4,747,894.
In an ultrasonic device, such as the 900 SERIES manufactured and marketed by Branson Ultrasonics Corporation, electrical energy is converted to mechanical energy--vibration--through a converter. The converter is attached to an acoustical horn (similar in concept to a tuning fork) which contacts and transmits the vibratory energy of the converter to the workpiece. This vibration manifests itself as heat induced by friction between the pieces to be joined, whereby the plastic at the joint briefly becomes molten. When the molten plastic solidifies, a strong molecular bond results.
Previously known methods of applying ultrasonic devices have been limited to welding similar materials, generally plastics. While ultrasonic apparatus have been used for embedding a material in a dissimilar base material, such apparatus have not heretofore been used for sealing food or tobacco product containers comprised of a thermoplastic portion and a non-thermoplastic portion. Furthermore, previously known packaging machines employing ultrasonics for thermoplastics have been slowed by the need to reposition a work piece to complete a welding or fastening task where the workpiece presented a complicated geometry.
In view of the foregoing, it is therefore an object of the present invention to provide a method and apparatus for sealing a food or tobacco product container comprised of dissimilar materials, i.e., having a thermoplastic portion and a non-thermoplastic portion, with an apparatus using an ultrasonic device.
It is further object of the present invention to provide a method and apparatus for sealing a food or tobacco product container comprised of is similar materials without the use of conventional wet glues, so that the sealed container may be carried by automated handling in a time period substantially shorter than that required when handling containers sealed with conventional glues.
It is another object of this invention to provide a method and apparatus for sealing such packages which is cleaner than the previously known method employing conventional wet glues.
It is still another object of present invention to provide an apparatus for sealing a food or tobacco product container using an ultrasonic device which obviates the need to reposition the workpiece on the apparatus when sealing a container having a complicated geometry and which apparatus is therefore capable of improved throughput than would otherwise be possible.